mYra wrote:

I am sorry if I'm posting something that has been already discussed.

A good question is whether this is in the FAQ. I must look in there sometime myself (:-))

Does human race broadcast some strong signals at the frequencies that
are scanned by SETI? If some extra-terrestrials had a project similar
to SETI, would they have a chance to find us?

Yes, but very briefly in the past. The transmissions were too brief and too poorly done to be useful. They were just a Media Public Relations exercise. There is a commercial "beam your name into space" project that is just an 'exercise to get funds'.

The full short answer is "No, nothing useful".

If not, why do we assume that they broadcast on such frequencies?

We make assumptions on what aliens would do to be DELIBERATELY found. One good assumption is to find a common 'special place' to look. We consider the 'Water Hole' to be a very special place.


And as to whether we should broadcast, good comments are given in:

http://home.earthlink.net/~jsgaravelli/MYTALK.HTML
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Just as it is in the best interest of a relatively young civilization to learn "at a distance" from a relatively advanced one, a relatively advanced one will gain nothing from a relatively younger one but the knowledge that it exists. Directed high-power transmission is expensive and they may not be worth talking to unless exploitation is a serious option. The reason why any concern about exploitation can be discounted is that, so far as we are aware, there is nothing we have that would be worth the time and expense for someone to come here and exploit.
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Regards,
Martin